The easiest way is to edit the file C:\WINDOWS\system32\drivers\etc\hosts with any text editor.
Opening it in a text editor, we add lines like the following:
127.0.0.1 vkontakte.ru 127.0.0.1 vk.com 127.0.0.1 ok.ru 127.0.0.1 odnoklassniki.ru 127.0.0.1 facebook.com
Save the changes to the file.
Similarly, you can block access to other sites.
After editing, you can change the attributes of the file by clicking on it with the right mouse button and ticking “Read Only”, “Hidden”. Click “OK” to apply the changes. Now the file cannot be edited without unchecking the “Read Only” checkbox and it will be invisible until you check the “Show hidden files and folders” checkbox in the “Control Panel” in the “Folder Options”.
I note that some antiviruses and anti-virus utilities can return the hosts file to the standard state.